Enhance the vendor script to build the libraries

Change-Id: I9e018591dc04ad1b79634f5d3164ae3d8ca13cfd
Reviewed-on: https://swiftshader-review.googlesource.com/3060
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Greg Hartman <ghartman@google.com>